Diseases are often described and studied in isolation of other disease states, yet many individuals have multiple chronic conditions occurring together (MCC). Defined as having at least three chronic conditions, MCC is highly prevalent among elderly Americans. Persons with MCC have a higher risk for avoidable hospitalizations and preventable complications while hospitalized. Depression is one of the most common co-occurring illnesses in those with MCC. Most patients with depression are initially treated in primary care (PC), and collaborative care models for depression have been shown to improve care processes and outcomes for depression patients treated in PC. The value of depression disease management models for patients with MCC is less clear. No studies have explicitly considered the effect of depression care management for persons with depression plus 2 or more comorbid conditions. We propose to develop a schema to help prioritize which depression patients most need depression care management, and help identify depression-MCC clusters that may be appropriate candidates for the development of multiple condition disease management programs. The objective of this study is to examine, for persons with depression, the effect of various groups of chronic diseases (clusters of MCC) on the likelihood of receipt of evidence-based depression treatment through 3 specific aims: (1) Compare the proportion of patients in each depression-MCC cluster that receive evidence-based depression care;(2) Determine the extent to which type of clinical care received (PC only versus shared mental health or other specialty care) mediates the relationship between depression-MCC and receipt of evidence-based depression treatment;(3) Assess the extent to which patient and system factors mediate or moderate the relationship between depression-MCC and receipt of evidence-based depression treatment. This study will employ a retrospective cohort design and use administrative data from the Veteran Health Administration (VA) and the Medicare Current Beneficiary Survey. Elderly persons with 8 highly prevalent and/or high cost chronic conditions that commonly co-occur with depression will be identified. Bivariate and multivariate methods will be used to determine the relationships between depression-MCC clusters and receipt of guideline-concordant depression treatment as well as the extent to which the type of clinical care received and other patient and system factors mediate/moderate the relationship between depression-MCC cluster and quality depression care.